This invention relates generally to turbochargers for motor vehicles and, more specifically, to means for progressively varying the A/R (Area/Radius) ratio of a turbocharger.
Turbochargers are well known devices used in all forms of vehicles for supplying air to the intake of an internal combustion engine at pressures above atmospheric pressure (“boost pressures”). A conventional turbocharger includes a turbine rotor or wheel with a plurality of fins or blades inside a volute turbine housing. The turbine rotor is rotated by exhaust gases from the engine which impinge upon the turbine blades. The rotor, via a connecting shaft, provides the driving torque to a compressor. Ambient air fed to the compressor creates a boost pressure that is fed to the intake manifold of the engine.
The flow capacity of the exhaust turbine is a function of the housing volute areas and the passage of the exhaust gases as it strikes the turbine blades. The flow of exhaust gas has to be regulated to control the compressor speed to create the desired boost in manifold pressure. A typical centrifugal compressor includes an impeller driven at high speed by the turbine rotor. A diffuser surrounding the impeller causes the ambient air to increase in pressure which is directed to the intake manifold.
One particular goal with any turbocharger is the need for a quick response, i.e., prevent “turbo lag,” a delay between the time when high power output is first demanded of the engine by setting the throttle to a wide open position and the time when a boost in the inlet manifold air pressure is delivered by the compressor. In some instances turbo lag could result in a dangerous driving situation when substantially instantaneous response is desired. If the turbocharger is large enough to provide the maximum horsepower for an internal combustion engine, then it will have excessive and potentially unsafe lag when the throttle is increased. If the turbocharger is reduced in size to minimize turbo lag, then efficiency is lost at higher engine rpms.
Some early turbocharger designs sought to solve the problem of turbo lag within a certain range of low engine speeds, such as when the engine is idling, by adding a regulated air supply to increase the mass of air entering the turbocharger intake and being forced into the engine manifold. At idle speed, the engine exhaust is insufficient to maintain the speed and charging-air output of the compressor section of the turbocharger, causing the turbocharger to “lag behind” the engine in performance. To maintain the speed of the turbocharger, a pair of nozzles penetrates the housing in opposite directions and injects air generally tangentially to the outer tips of the rotor blades. The air pressure provided by the nozzles acts as a “jet assist” in the turbocharger compressor when the engine is at idling speed (see U.S. Pat. No. 3,190,068 to Williams et al., Turbocharger for Compressor Driving Engine, issued Jun. 22, 1965, and U.S. Pat. No. 3,363,412, to Fischer et al., System for Maintaining Turbocharger Compressor Speed, issued Jan. 16, 1968). Another design positions nozzles at preselected points about the turbine rotor and directs air through the nozzles to impinge the blades and, in addition to providing a jet assist, prevent resonant vibration conditions in the rotor for its entire rotational speed range (see U.S. Pat. No. 3,396,534 to Bernson et al., Air Impingement Nozzle Arrangement for a Turbocharger Compressor and an Improved Method of Employing Air Impingement, issued Aug. 13, 1968).
The air-assisted designs do not operate to minimize turbo lag when the turbocharger is already in a spun-up condition and the engine is at normal operating speed but requires additional horsepower. Furthermore, the air-assisted designs require a waste gate to handle the total exhaust flow at maximum horsepower.
Other designs have proposed variable volute turbines; variable geometry turbines; electrically driven turbines; moveable or pivoting vanes, gates and walls for guiding, dividing, or changing the direction the exhaust gases relative to the turbine rotor and thereby control its rotational speed.
Variable volute turbines make use of a sliding or flexible dividing wall to change the geometry of the volute and, therefore, the flow of exhaust gas into the turbine wheel One example of a variable volute design is U.S. Pat. No. 4,177,005 to Bozung. The design can be slow in responding to sudden changes, is used solely as a braking application, and its performance can be negatively affected by debris build-up on the sliding wall surfaces. Another example is US 2011/0052374 to Arnold. This design makes use of a flexible dividing wall that moves along a path to vary the discharge area into the turbine wheel. The design is complicated and failure-prone because the chain and bearing mechanism used to move the wall are in the path of the hot exhaust flow.
Variable geometry turbochargers use adjustable guide vanes arranged about the turbine wheel in order to control exhaust gas flow to the wheel. These designs require a large number of expensive components along with sophisticated software and controls.
Electrically driven turbines essentially turn the shaft of the turbine rotor into an armature. Because the armature must be disengaged once the turbine rotor spins up to a certain speed, these designs entail complicated electro-mechanical structures.
A moveable wall design for a variable geometry turbocharger is disclosed in US 2012/0036849A1 to Watson et al. (“the Watson publication”). A pivoting wall located along the upper wall of the housing pivots about a point located upstream of the housing tongue and near the entry to the housing (compare U.S. 2010/0266390 to Henderson et al. showing a pivoting wall located far downstream of the tongue). As the wall pivots away from the upper wall, the wall reduces the volume of exhaust gas flowing into the volute. Alternatively, a rotating wedge segment can be located along the upper wall of the housing and moved downstream to alter the cross section of the volute. However, neither the wall nor the wedge can prevent exhaust air from flowing into the turbine wheel even when fully closed or deployed, nor can either one alter or extend the end of the housing tongue. Additionally, an equal amount of exhaust cannot flow over and under of the pivoting wall or wedge because there is no neutral position.
A moveable or variable vane design, which is intended to minimize the occurrence of turbo lag, is described in U.S. Pat. No. 7,481,056 to Blaylock et al., Turbocharger with Adjustable Throat, issued Jan. 27, 2009 (“Blaylock”). A flow control gate is positioned in the center of the inlet to the housing on the exhaust side of the turbocharger and adapted, from a command, to momentarily rotate or pivot downstream about a transverse hinge from a neutral first position to a second position toward the blades of the turbine rotor. (There is no open position above the neutral position.) In the second position, the control gate reduces the volume of exhaust gas flowing along an inner flow path toward the turbine rotor and increases the air velocity and pressure upon the turbine rotor. This causes the turbocharger to reach optimal operating speed to substantially reduce or eliminate harmful emissions while increasing initial engine takeoff power and reducing lag time from when speedup was first signaled by the operator. Once the turbine is spun up, the control gate returns to a neutral position. When in the neutral position, the operation of the turbocharger is as a standard turbocharger. The typical time for the gate action is a very small part of a second before returning to the neutral position. A properly sized turbocharger could eliminate the need for a waste gate and the turbocharger could be large enough to handle the total exhaust flow at maximum horsepower.
Still others have mechanically coupled the turbocharger to the engine. This type of arrangement, called “turbocompounding,” is described in the September 2010, North American edition of the trade magazine, Diesel Progress (see “Could SuperTurbocharger Become the Hero on Fuel Economy?”). The turbocharger adds a small additional horsepower boost through the combination of the turbocharger and its transmission. However, turbocompounding entails complexity and involves additional production cost all in hopes of achieving at most a 7% fuel savings on diesel engines.
A flow control gate which momentarily alters the A/R (Area/Radius) ratio of a turbocharger in order to eliminate turbo lag is desirable (compare DE 31 05 179 A1 which discloses a gate that lies along the outer wall of the housing and outside the inlet or throat section and, therefore, cannot alter the A/R ratio of the housing). It is well known in the art that the A/R ratio is the inlet cross sectional area dived by the radius from the turbo centerline to the centroid of that area. The inlet (or throat section) of a turbocharger extends between the end of the housing which mounts to the exhaust manifold and the tip or end of the tongue of the housing. To calculate the A/R ratio,                the area of the turbine housing is measured in square inches of a cutting plane line that passes through the turbine's gas passage at the tip of the tongue, divided by the radius from the center of the turbine wheel's axis of rotation, to the centroid of the volute. The tongue tip is the entry point of the turbine housing where exhaust gas flow begins to reach the turbine wheel inducer.(see Jay K. Miller, Turbo: Real World High Performance Turbocharger Systems 45 (CarTech 2008)).        
From the above, it is clear that:                1. The “A” in the A/R ratio is determined by the cross-sectional area defined by a cutting plane line that passes through the turbine's gas passage at the tip of the tongue to the opposing wall of the inlet channel;        2. The inlet area A can be changed by making a new housing with a different sized area A; and        3. The throat or inlet extends to the end of the tongue but not beyond it.        
The ability to alter the area of the inlet is important. For example, reducing the throat cross-section results in higher boost pressures. Turbocharger housings are designed with different A/R ratios along with complicated means (e.g., variable geometry turbines) to achieve the desired performance. Other than Blaylock's flow control gate which attempts to adjust the throat, the A/R ratio in prior art pivoting vane designs remains fixed because, absent making a new housing, there is no way for those designs to alter either the throat area or the radius from the center of the turbine wheel. However, Blaylock cannot alter where the tongue tip or tongue end of the housing begins and ends in real time and, because of the location of the pivot point (at about the center of the vane), cannot close flow completely.